#include<stdio.h>
int main()
{
	int i,ch;
	while ((ch = getchar()) != EOF)
	{
		if ((ch >= 'A' && ch <= 'Z') || (ch >= 'a' && ch <= 'z'))
			printf("YES");
		else
			printf("NO");
		printf("\n");
		getchar();
	}
	return 0;
}